Internet DRAFT - draft-bonica-spring-srv6-plus
draft-bonica-spring-srv6-plus
SPRING Working Group R. Bonica
Internet-Draft S. Hegde
Intended status: Standards Track Juniper Networks
Expires: April 17, 2020 Y. Kamite
NTT Communications Corporation
A. Alston
D. Henriques
Liquid Telecom
L. Jalil
Verizon
J. Halpern
Ericsson
J. Linkova
Google
G. Chen
Baidu
October 15, 2019
Segment Routing Mapped To IPv6 (SRm6)
draft-bonica-spring-srv6-plus-06
Abstract
This document describes Segment Routing mapped to IPv6 (SRm6). SRm6
is a Segment Routing (SR) solution that leverages IPv6. It supports
a wide variety of use-cases while remaining in strict compliance with
IPv6 specifications. SRm6 is optimized for ASIC-based forwarding
devices that operate at high data rates.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 17, 2020.
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Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
3. Paths, Segments And Instructions . . . . . . . . . . . . . . 5
4. Segment Types . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Adjacency Segments . . . . . . . . . . . . . . . . . . . 6
4.2. Node Segments . . . . . . . . . . . . . . . . . . . . . . 7
4.3. Binding Segments . . . . . . . . . . . . . . . . . . . . 7
5. Segment Identifiers (SID) . . . . . . . . . . . . . . . . . . 8
5.1. Range . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5.2. Assigning SIDs to Adjacency Segments . . . . . . . . . . 10
5.3. Assigning SIDs to Node Segments . . . . . . . . . . . . . 11
5.4. Assigning SIDs to Binding Segments . . . . . . . . . . . 11
6. Service Instructions . . . . . . . . . . . . . . . . . . . . 11
6.1. Per-Segment . . . . . . . . . . . . . . . . . . . . . . . 11
6.2. Per-Path . . . . . . . . . . . . . . . . . . . . . . . . 12
7. The IPv6 Data Plane . . . . . . . . . . . . . . . . . . . . . 12
7.1. The Routing Header . . . . . . . . . . . . . . . . . . . 13
7.2. The Destination Options Header . . . . . . . . . . . . . 14
8. Control Plane . . . . . . . . . . . . . . . . . . . . . . . . 15
9. Differences Between SRv6 and SRv6+ . . . . . . . . . . . . . 15
9.1. Routing Header Size . . . . . . . . . . . . . . . . . . . 15
9.2. Decoupling of Topological and Service Instructions . . . 17
9.3. Authentication . . . . . . . . . . . . . . . . . . . . . 17
9.4. Traffic Engineering Capability . . . . . . . . . . . . . 18
9.5. IP Addressing Architecture . . . . . . . . . . . . . . . 18
10. Compliance . . . . . . . . . . . . . . . . . . . . . . . . . 18
11. Operational Considerations . . . . . . . . . . . . . . . . . 19
11.1. Ping and Traceroute . . . . . . . . . . . . . . . . . . 19
11.2. ICMPv6 Rate Limiting . . . . . . . . . . . . . . . . . . 19
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
13. Security Considerations . . . . . . . . . . . . . . . . . . . 19
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14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
15.1. Normative References . . . . . . . . . . . . . . . . . . 19
15.2. Informative References . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
1. Overview
Network operators deploy Segment Routing (SR) [RFC8402] so that they
can forward packets through SR paths. An SR path provides
unidirectional connectivity from its ingress node to its egress node.
While an SR path can follow the least cost path from ingress to
egress, it can also follow any other path.
An SR path contains one or more segments. A segment provides
unidirectional connectivity from its ingress node to its egress node.
It includes a topological instruction that controls its behavior.
The topological instruction is executed on the segment ingress node.
It determines the segment egress node and the method by which the
segment ingress node forwards packets to the segment egress node.
Per-segment service instructions can augment a segment. Per-segment
service instructions, if present, are executed on the segment egress
node.
Likewise, a per-path service instruction can augment a path. The
per-path service instruction, if present, is executed on the path
egress node. Section 3 of this document illustrates the relationship
between SR paths, segments and instructions.
A Segment Identifier (SID) identifies each segment. Because there is
a one-to-one relationship between segments and the topological
instructions that control them, the SID that identifies a segment
also identifies the topological instruction that controls it.
A SID is different from the topological instruction that it
identifies. While a SID identifies a topological instruction, it
does not contain the topological instruction that it identifies.
Therefore, a SID can be encoded in relatively few bits, while the
topological instruction that it identifies may require many more bits
for encoding.
An SR path can be represented by its ingress node as an ordered
sequence of SIDs. In order to forward a packet through an SR path,
the SR ingress node encodes the SR path into the packet as an ordered
sequence of SIDs. It can also augment the packet with service
instructions.
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Because the SR ingress node is also the first segment ingress node,
it executes the topological instruction associated with the first
segment. This causes the packet to be forwarded to the first segment
egress node. When the first segment egress node receives the packet,
it executes any per-segment service instructions that augment the
first segment.
If the SR path contains exactly one segment, the first segment egress
node is also the path egress node. In this case, that node executes
any per-path service instruction that augments the path, and SR
forwarding is complete.
If the SR path contains multiple segments, the first segment egress
node is also the second segment ingress node. In this case, that
node executes the topological instruction associated with the second
segment. The above-described procedure continues until the packet
arrives at the SR egress node.
In the above-described procedure, only the SR ingress node maintains
path information. Segment ingress and egress nodes maintain
information regarding the segments in which they participate, but
they do not maintain path information.
The SR architecture, described above, can leverage either an MPLS
[RFC3031] data plane or an IPv6 [RFC8200] data plane. SR-MPLS
[I-D.ietf-spring-segment-routing-mpls] leverages MPLS. SRv6
[I-D.ietf-spring-srv6-network-programming]
[I-D.ietf-6man-segment-routing-header] leverages IPv6.
This document describes Segment Routing mapped to IPv6 (SRm6). SRm6
is an SR variant that leverages IPv6. It supports a wide variety of
use-cases while remaining in strict compliance with IPv6
specifications. SRm6 is optimized for ASIC-based forwarding devices
that operate at high data rates. Section 9 of this document
highlights differences between SRv6 and SRm6.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
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3. Paths, Segments And Instructions
An SRm6 path is determined by the segments that it contains. It can
be represented by its ingress node as an ordered sequence of SIDs.
A segment is determined by its ingress node and by the topological
instruction that controls its behavior. The topological instruction
determines the segment egress node and the method by which the
segment ingress node forwards packets to the segment egress node.
Per-segment service instructions augment, but do not determine,
segments. A segment ingress node can:
o Send one packet through a segment with one per-segment service
instruction.
o Send another packet through the same segment with a different per-
segment service instruction.
o Send another packet through the same segment without any per-
segment service instructions.
Likewise, per-path service instructions augment, but do not
determine, paths.
---- ---- ---- ---- ---- ----
|Node|----|Node|----|Node|----|Node|----|Node|----|Node|
| A | | B | | C | | D | | E | | F |
---- ---- ---- ---- ---- ----
| | | |
-------------------| |-------------------|
Segment A-C |---------| Segment D-F
Segment C-D
| |
-------------------------------------------------
SRm6 Path
Figure 1: Paths, Segments And Instructions
Figure 1 depicts an SRm6 path. The path provides unidirectional
connectivity from its ingress node (i.e., Node A) to its egress node
(i.e., Node F). It contains Segment A-C, Segment C-D and Segment
D-F.
In Segment A-C, Node A is the ingress node, Node B is a transit node,
and Node C is the egress node. Therefore, the topological
instruction that controls the segment is executed on Node A, while
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per-segment service instructions that augment the segment (if any
exist) are executed on Node C.
In Segment C-D, Node C is the ingress node and Node D is the egress
node. Therefore, the topological instruction that controls the
segment is executed on Node C, while per-segment service instructions
that augment the segment (if any exist) are executed on Node D.
In Segment D-F, Node D is the ingress node, Node E is a transit node,
and Node F is the egress node. Therefore, the topological
instruction that controls the segment is executed on Node D, while
per-segment service instructions that augment the segment (if any
exist) are executed on Node F.
Node F is also the path egress node. Therefore, if a per-path
service instruction augments the path, it is executed on Node F.
Segments A-C, C-D and D-F are also contained by other paths that are
not included in the figure.
4. Segment Types
SRm6 supports the following segment types:
o Adjacency.
o Node.
o Binding.
Adjacency segments forward packets through a specified link that
connects the segment ingress node to the segment egress node. Node
segments forward packets through the least cost path from the segment
ingress node to the segment egress node. Binding segments facilitate
recursive application of SRm6. They cause SRm6 paths to be nested in
a hierarchy.
Each segment type is described below.
4.1. Adjacency Segments
When a packet is submitted to an adjacency segment, the topological
instruction associated with that segment operates upon the packet.
The topological instruction executes on the segment ingress node and
receives the following parameters:
o An IPv6 address that identifies an interface on the segment egress
node.
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o An interface identifier.
The topological instruction behaves as follows:
o If the interface that was received as a parameter is not
operational, discard the packet and send an ICMPv6 [RFC4443]
Destination Unreachable message (Code: 5, Source Route Failed) to
the packet's source node.
o Overwrite the packet's Destination Address with the IPv6 address
that was received as a parameter.
o Forward the packet through the above-mentioned interface.
For further processing details, see [I-D.bonica-6man-comp-rtg-hdr].
4.2. Node Segments
When a packet is submitted to a node segment, the topological
instruction associated with that segment operates upon the packet.
The topological instruction executes on the segment ingress node and
receives an IPv6 address as a parameter. The IPv6 address identifies
an interface on the segment egress node.
The topological instruction behaves as follows:
o If the segment ingress node does not have a viable route to the
IPv6 address received as a parameter, discard the packet and send
an ICMPv6 Destination Unreachable message (Code:1 Net Unreachable)
to the packet's source node.
o Overwrite the packet's Destination Address with the destination
address that was received as a parameter.
o Forward the packet to the next hop along the least cost path to
the segment egress node. If there are multiple least cost paths
to the segment egress node (i.e., Equal Cost Multipath), execute
procedures so that all packets belonging to a flow are forwarded
through the same next hop.
For further processing details, see [I-D.bonica-6man-comp-rtg-hdr].
4.3. Binding Segments
When a packet is submitted to a binding segment, the topological
instruction associated with that segment operates upon the packet.
The topological instruction executes on the segment ingress node and
receives the following parameters:
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o An IPv6 address.
o A SID list length.
o A SID list.
The topological instruction behaves as follows:
o If the segment ingress node does not have a viable route to the
IPv6 address received as a parameter, discard the packet and send
an ICMPv6 Destination Unreachable message (Code:1 Net Unreachable)
to the packet's source node.
o Prepend a Compressed Routing Header (CRH)
[I-D.bonica-6man-comp-rtg-hdr] to the packet. Copy the SID list
length, received as a parameter, to the CRH Segments Left field.
Also copy the SID list, received as a parameter, to the CRH SID
list.
o Prepend an IPv6 header to the packet. Copy the IPv6 address,
received as a parameter, to the IPv6 Destination Address.
o Forward the packet to the next hop along the least cost path to
the IPv6 address received as a parameter. If there are multiple
least cost paths to the IPv6 address received as a parameter
(i.e., Equal Cost Multipath), execute procedures so that all
packets belonging to a flow are forwarded through the same next
hop.
For further processing details, see [I-D.bonica-6man-comp-rtg-hdr].
5. Segment Identifiers (SID)
A Segment Identifier (SID) is an unsigned integer that identifies a
segment. Because there is a one-to-one relationship between segments
and the topological instructions that control them, the SID that
identifies a segment also identifies the topological instruction that
controls it.
A SID is different from the topological instruction that it
identifies. While a SID identifies a topological instruction, it
does not contain the topological instruction that it identifies.
Therefore, a SID can be encoded in relatively few bits, while the
topological instruction that it identifies may require many more bits
for encoding.
SIDs have node-local significance. This means that a segment ingress
node MUST identify each segment that it originates with a unique SID.
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However, a SID that is used by one segment ingress node to identify a
segment that it originates can be used by another segment ingress
node to identify another segment. For example, SID S can identify
both of the following:
o A segment whose ingress is Node A and whose egress is Node Z.
o Another segment whose ingress is Node B and whose egress is also
node Z.
Although SIDs have node-local significance, an SRm6 path can be
uniquely identified by its ingress node and an ordered sequence of
SIDs. This is because the topological instruction associated with
each segment determines the ingress node of the next segment (i.e.,
the node upon which the next SID has significance.)
SIDs can be assigned in a manner that simplifies network operations.
See Section 5.2 and Section 5.3 for details.
5.1. Range
SID values range from 0 to a configurable Maximum SID Value (MSV).
The values 0 through 15 are reserved for future use. The following
are valid MSVs:
o 65,535 (i.e., 2**16 minus 1).
o 4,294,967,295 (i.e., 2**32 minus 1).
In order to optimize packet encoding (Section 7.1), network operators
can configure all nodes within an SRm6 domain to have the smallest
feasible MSV. The following paragraphs explain how an operator
determines the smallest feasible MSV.
Consider an SRm6 domain that contains 5,000 nodes connected to one
another by point-to-point infrastructure links. The network topology
is not a full-mesh. In fact, each node supports 200 point-to-point
infrastructure links or fewer. Given this SRm6 domain, we will
determine the smallest feasible MSV under the following conditions:
o The SRm6 domain contains adjacency segments only.
o The SRm6 domain contains node segments only.
o The SRm6 domain contains both adjacency and node segments.
If an SRm6 domain contains adjacency segments only, and each node
creates a adjacency segment to each of its neighbors, each node will
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create 200 segments or fewer and consume 200 SIDs or fewer. This is
because each node has 200 neighbors or fewer. Because SIDs have
node-local significance (i.e., they can be reused across nodes), the
smallest feasible MSV is 65,535.
Adding nodes to this SRm6 domain will not increase the smallest
feasible MSV, so long as each node continues to support 65,519 point-
to-point infrastructure links or fewer. If a single node is added to
the domain and that node supports 65,520 infrastructure links, the
smallest feasible MSV will increase to 4,294,967,295.
If an SRm6 domain contains node segments only, and every node creates
a node segment to every other node, every node will create 4,999
segments and consume 4,999 SIDs. This is because the domain contains
5,000 nodes. Because SIDs have node-local significance (i.e., they
can be reused across nodes), the smallest feasible MSV is 65,535.
Adding nodes to this SRm6 domain will not increase the smallest
feasible MSV until the number of nodes exceeds 65,519. When the
smallest feasible MSV increases, it becomes 4,294,967,295.
If an SRm6 domain contains both adjacency and node segments, each
node will create 5,199 segments or fewer and consume 5,199 SIDs or
fewer. This value is the sum of the following:
o The number of node segments that each node will create, given that
every node creates a node segment to every other node (i.e.,
4,999).
o The number of adjacency segments that each node will create, given
that each node creates a adjacency segment to each of its
neighbors (i.e., 200 or fewer).
Because SIDs have node-local significance (i.e., they can be reused
across nodes), the smallest feasible MSV is 65,535.
Adding nodes to this SRm6 domain will not increase the smallest
feasible MSV until the number of nodes plus the maximum number of
infrastructure links per node exceeds 65,519. When the smallest
feasible MSV increases, it becomes 4,294,967,295.
5.2. Assigning SIDs to Adjacency Segments
Network operators can establish conventions by which they assign SIDs
to adjacency segments. These conventions can simplify network
operations.
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For example, a network operator can reserved a range of SIDs for
adjacency segments. It can further divide that range into subranges,
so that all segments sharing a common egress node are identified by
SIDs from the same subrange.
5.3. Assigning SIDs to Node Segments
In order to simplify network operations, all node segments that share
a common egress node are identified by the same SID. In order to
maintain this discipline, network wide co-ordination is required.
For example, assume that an SRm6 domain contains N nodes. Network
administrators reserve a block of N SIDs and configure one of those
SIDs on each node. Each node advertises its SID into the control
plane. When another node receives that advertisement, it creates a
node segment between itself and the advertising node. It also
associates the SID that it received in the advertisement with the
newly created segment. See [I-D.bonica-lsr-crh-isis-extensions] for
details.
5.4. Assigning SIDs to Binding Segments
Network operators can establish conventions by which they assign SIDs
to binding segments. These conventions can simplify network
operations.
For example, a network operator can reserve a range of SIDs for
binding segments. It can further divide that range into subranges,
so that all segments sharing a common egress node are identified by
SIDs from the same subrange.
6. Service Instructions
SRm6 supports the following service instruction types:
o Per-segment.
o Per-path.
Each is described below.
6.1. Per-Segment
Per-segment service instructions can augment a segment. Per-segment
service instructions, if present, are executed on the segment egress
node. Because the path egress node is also a segment egress node, it
can execute per-segment service instructions.
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The following are examples of per-segment service instructions:
o Expose a packet to a firewall policy.
o Expose a packet to a sampling policy.
Per-segment Service Instruction Identifiers identify a set of service
instructions. Per-segment Service Instruction Identifiers are
allocated and distributed by a controller. They have domain-wide
significance.
6.2. Per-Path
A per-path service instruction can augment a path. The per-path
service instruction, if present, is executed on the path egress node.
The following are examples of per-path service instructions:
o De-encapsulate a packet and forward its newly exposed payload
through a specified interface.
o De-encapsulate a packet and forward its newly exposed payload
using a specified routing table.
Per-path Service Instruction Identifiers identify per-path service
instructions. Per-path Service Instruction Identifiers are allocated
and distributed by the processing node (i.e., the path egress node).
They have node-local significance. This means that the path egress
node MUST allocate a unique Per-path Service Instruction Identifier
for each per-path service instruction that it instantiates.
7. The IPv6 Data Plane
SRm6 ingress nodes generate IPv6 header chains that represent SRm6
paths. An IPv6 header chain contains an IPv6 header. It can also
contain one or more extension headers.
An extension header chain that represents an SRm6 path can contain
any valid combination of IPv6 extension headers. The following
bullet points describe how SRm6 leverages IPv6 extension headers:
o If an SRm6 path contains multiple segments, the IPv6 header chain
that represents it MUST contain a Routing header. The SRm6 path
MUST be encoded in the Routing header as an ordered sequence of
SIDs.
o If an SRm6 path is augmented by a per-path service instruction,
the IPv6 header chain that represents it MUST contain a
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Destination Options header. The Destination Options header MUST
immediately precede an upper-layer header and it MUST include a
Per-Path Service Instruction Identifier.
o If an SRm6 path contains a segment that is augmented by a per-
segment service instruction, the IPv6 chain that represents it
MUST contain a Routing header and a Destination Options header.
The Destination Options header MUST immediately precede a Routing
header and it MUST include the Per-Segment Service Instruction
Identifier.
The following subsections describe how SRm6 uses the Routing header
and the Destination Options header.
7.1. The Routing Header
SRm6 defines two new Routing header types. Generically, they are
called the Compressed Routing Header (CRH)
[I-D.bonica-6man-comp-rtg-hdr]. More specifically, the 16-bit
version of the CRH is called the CRH-16, while the 32-bit version of
the CRH is called the CRH-32.
Both CRH versions contain the following fields:
o Next Header - Identifies the header immediately following the CRH.
o Hdr Ext Len - Length of the CRH.
o Routing Type - Identifies the Routing header variant (i.e., CRH-16
or CRH-32).
o Segments Left - The number of segments still to be traversed
before reaching the path egress node.
o SID List - Represents the SRm6 path as an ordered list of SIDs.
SIDs are listed in reverse order, with SID[0] representing the
final segment, SID[1] representing the penultimate segment, and so
forth. SIDs are listed in reverse order so that Segments Left can
be used as an index to the SID List. The SID indexed by Segments
Left is called the current SID.
In the CRH-16, each SID list entry is encoded in 16-bits. In the
CRH-32, each SID list entry is encoded in 32-bits. In networks where
the smallest feasible MSV (Section 5.1) is greater than 65,635,
CRH-32 is required. Otherwise, CRH-16 is preferred.
As per [RFC8200], when an IPv6 node receives a packet, it examines
the packet's destination address. If the destination address
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represents an interface belonging to the node, the node processes the
next header. If the node encounters and recognizes the CRH, it
processes the CRH as follows:
o If Segments Left equal 0, skip over the CRH and process the next
header in the packet.
o Decrement Segments Left.
o Search for the current SID in a local table that maps SID's to
topological instructions. If the current SID cannot be found in
that table, send an ICMPv6 Parameter Problem message to the
packet's Source Address and discard the packet.
o Execute the topological instruction found in the table as
described in Section 4. This causes the packet to be forwarded to
the segment egress node.
When the packet arrives at the segment egress node, the above-
described procedure is repeated. For further processing details, see
[I-D.bonica-6man-comp-rtg-hdr].
7.2. The Destination Options Header
According to [RFC8200], the Destination Options header contains one
or more IPv6 options. It can occur twice within a packet, once
before a Routing header and once before an upper-layer header. The
Destination Options header that occurs before a Routing header is
processed by the first destination that appears in the IPv6
Destination Address field plus subsequent destinations that are
listed in the Routing header. The Destination Options header that
occurs before an upper-layer header is processed by the packet's
final destination only.
Therefore, SRm6 defines the following new IPv6 options:
o The SRm6 Per-Segment Service Instruction Option
[I-D.bonica-6man-seg-end-opt]
o The SRm6 Per-Path Service Instruction Option
[I-D.bonica-6man-vpn-dest-opt]
The SRm6 Per-Segment Service Instruction Option is encoded in a
Destination Options header that precedes the CRH. Therefore, it is
processed by every segment egress node. It includes a Per-Segment
Service Instruction Identifier and causes segment egress nodes to
execute per-segment service instructions.
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The SRm6 Per-Path Service Instruction Option is encoded in a
Destination Options header that precedes the upper-layer header.
Therefore, it is processed by the path egress node only. It includes
a Per-Path Service Instruction Identifier and causes the path egress
node to execute a per-path service instruction.
8. Control Plane
IS-IS extensions [I-D.bonica-lsr-crh-isis-extensions] have been
defined for the following purposes:
o So that SRm6 segment ingress nodes can flood information regarding
adjacency segments that they originate.
o So that SRm6 segment egress nodes can flood information regarding
node segments that they terminate.
BGP extensions [I-D.ssangli-idr-bgp-vpn-srv6-plus] are defined so
that SRm6 path egress nodes can associate path-terminating service
instructions with Network Layer Reachability Information (NLRI).
Additional BGP extensions [I-D.alston-spring-crh-bgp-signalling] are
defined so that SIDs can be mapped to the IPv6 addresses that they
represent.
9. Differences Between SRv6 and SRv6+
9.1. Routing Header Size
SRv6 defines a Routing header type, called the Segment Routing Header
(SRH). The SRH contains a field that represents the SRv6 path as an
ordered sequence of SIDs. Each SID contained by that field is 128
bits long.
Likewise, SRm6 defines two Routing Header Types, called CRH-16 and
CRH-32. Both contain a field that represents the SRv6 path as an
ordered sequence of SIDs. In the CRH-16, each SID is 16 bits long.
In the CRH-32, each SID is 32 bits long.
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+------+------------------------+-------------+-------------+
| SIDs | SRv6 SRH (128-bit SID) | SRm6 CRH-16 | SRm6 CRH-32 |
+------+------------------------+-------------+-------------+
| 1 | 24 | 8 | 8 |
| 2 | 40 | 8 | 16 |
| 3 | 56 | 16 | 16 |
| 4 | 72 | 16 | 24 |
| 5 | 88 | 16 | 24 |
| 6 | 104 | 16 | 32 |
| 7 | 120 | 24 | 32 |
| 8 | 136 | 24 | 40 |
| 9 | 152 | 24 | 40 |
| 10 | 168 | 24 | N/A |
| 11 | 184 | 32 | N/A |
| 12 | 200 | 32 | N/A |
| 13 | 216 | 32 | N/A |
| 14 | 232 | 32 | N/A |
| 15 | 248 | 40 | N/A |
| 16 | 264 | 40 | N/A |
| 17 | 280 | 40 | N/A |
| 18 | 296 | 40 | N/A |
+------+------------------------+-------------+-------------+
Table 1: Routing Header Size (in Bytes) As A Function Of Routing
Header Type and Number Of SIDs
Table 1 reflects Routing header size as a function of Routing header
type and number of SIDs contained by the Routing header. Due to
their relative immaturity,
[I-D.filsfils-spring-net-pgm-extension-srv6-usid],
[I-D.li-spring-compressed-srv6-np] and
[I-D.mirsky-6man-unified-id-sr] are omitted from this analysis.
Large Routing headers are undesirable for the following reasons:
o Many ASIC-based forwarders copy the entire IPv6 extension header
chain from buffer memory to on-chip memory. As the size of the
IPv6 extension header chain increases, so does the cost of this
copy.
o Because Path MTU Discovery (PMTUD) [RFC8201] is not entirely
reliable, many IPv6 hosts refrain from sending packets larger than
the IPv6 minimum link MTU (i.e., 1280 bytes). When packets are
small, the overhead imposed by large Routing headers becomes
pronounced.
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9.2. Decoupling of Topological and Service Instructions
SRm6 decouples topological instructions from service instructions.
Topological instructions are invoked at the segment ingress node, as
a result of CRH processing, while service instructions are invoked at
the segment egress node, as a result of Destination Option
processing. Therefore, network operators can use SRm6 mechanisms to
support topological instructions, service instructions, or both.
---------- ---------- ----------
| Ethernet | | Ethernet | | Ethernet |
---------- ---------- ----------
Service | VXLAN | | Dest | | Dest |
Instruction ---------- | | | |
| UDP | | Option | | Option |
---------- ---------- ----------
Topological | | | | |
Instructions | CRH | | | | CRH |
---------- | | ----------
| IPv6 | | IPv6 | | IPv6 |
---------- ---------- ----------
Option 1 Option 2 Option 3
Figure 2: EVPN Design Alternatives
Figure 2 illustrates this point by depicting design options available
to network operators offering Ethernet Virtual Private Network
[RFC7432] services over Virtual eXtensible Local Area Network (VXLAN)
[RFC7348]. In Option 1, the network operator encodes topological
instructions in the CRH, while encoding service instructions in a
VXLAN header. In Option 2, the network operator encodes service
instructions in a Destination Options header, while allowing traffic
to traverse the least cost path between the ingress and egress
Provider Edge (PE) routers. In Option 3, the network operator
encodes topological instructions in the CRH, and encodes service
instructions in a Destination Options header.
9.3. Authentication
The IPv6 Authentication Header (AH) [RFC4302] can be used to
authenticate SRm6 packets. However, AH processing is not defined in
SRv6.
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9.4. Traffic Engineering Capability
SRm6 supports traffic engineering solutions that rely exclusively
upon adjacency segments. For example, consider an SRm6 network whose
diameter is 12 hops and whose minimum feasible MSV is 65,525. In
that network, in the worst case, SRm6 overhead is 72 bytes (i.e., a
40-byte IPv6 header and a 32-byte CRH-16).
SRv6 also supports traffic engineering solutions that rely
exclusively upon adjacency segments (i.e., END.X SIDs). However,
SRv6 overhead may be prohibitive. For example, consider an SRv6
network whose diameter is 12 hops. In the worst case, SRv6 overhead
is 240 bytes (i.e., a 40 byte IPv6 header and a 200-byte SRH).
9.5. IP Addressing Architecture
In SRv6, an IPv6 address can represent either of the following:
o A network interface
o An instruction instantiated on a node (i.e., an SRv6 SID)
In SRm6 an IPv6 address always represents a network interface, as per
[RFC4291].
10. Compliance
In order to be compliant with this specification, an SRm6
implementation MUST:
o Be able to process IPv6 options as described in Section 4.2 of
[RFC8200].
o Be able to process the Routing header as described in Section 4.4
of [RFC8200].
o Be able to process the Destination Options header as described in
Section 4.6 of [RFC8200].
o Support the CRH-16 and the CRH-32
Additionally, an SRm6 implementation MAY:
o Recognize the Per-Segment Service Instruction Option.
o Recognize the Per-Path Service Instruction Option.
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11. Operational Considerations
11.1. Ping and Traceroute
Ping and Traceroute [RFC2151] both operate correctly in SRm6 (i.e.,
in the presence of the CRH).
11.2. ICMPv6 Rate Limiting
As per [RFC4443], SRm6 nodes rate limit the ICMPv6 messages that they
emit.
12. IANA Considerations
SID values 0-15 are reserved for future use. They may be assigned by
IANA, based on IETF Consensus.
IANA is requested to establish a "Registry of SRm6 Reserved SIDs".
Values 0-15 are reserved for future use.
13. Security Considerations
SRm6 domains MUST NOT span security domains. In order to enforce
this requirement, security domain edge routers MUST do one of the
following:
o Discard all inbound SRm6 packets whose IPv6 destination address
represents domain infrastructure.
o Authenticate [RFC4302] [RFC4303] all inbound SRm6 packets whose
IPv6 destination address represents domain infrastructure.
14. Acknowledgements
The authors wish to acknowledge Dr. Vanessa Ameen, Reji Thomas, Parag
Kaneriya, Rejesh Shetty, Nancy Shaw, and John Scudder.
15. References
15.1. Normative References
[I-D.alston-spring-crh-bgp-signalling]
Alston, A., Henriques, D., and R. Bonica, "BGP Extensions
for IPv6 Compressed Routing Header (CRH)", draft-alston-
spring-crh-bgp-signalling-01 (work in progress), July
2019.
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[I-D.bonica-6man-comp-rtg-hdr]
Bonica, R., Kamite, Y., Niwa, T., Alston, A., Henriques,
D., So, N., Xu, F., Chen, G., Zhu, Y., Yang, G., and Y.
Zhou, "The IPv6 Compressed Routing Header (CRH)", draft-
bonica-6man-comp-rtg-hdr-07 (work in progress), September
2019.
[I-D.bonica-6man-seg-end-opt]
Bonica, R., Halpern, J., Kamite, Y., Niwa, T., So, N., Xu,
F., Chen, G., Zhu, Y., Yang, G., and Y. Zhou, "The Per-
Segment Service Instruction (PSSI) Option", draft-bonica-
6man-seg-end-opt-04 (work in progress), July 2019.
[I-D.bonica-6man-vpn-dest-opt]
Bonica, R., Kamite, Y., Lenart, C., So, N., Xu, F.,
Presbury, G., Chen, G., Zhu, Y., Yang, G., and Y. Zhou,
"The Per-Path Service Instruction (PPSI) Option", draft-
bonica-6man-vpn-dest-opt-06 (work in progress), July 2019.
[I-D.bonica-lsr-crh-isis-extensions]
Kaneriya, P., Shetty, R., Hegde, S., and R. Bonica, "IS-IS
Extensions To Support The IPv6 Compressed Routing Header
(CRH)", draft-bonica-lsr-crh-isis-extensions-00 (work in
progress), May 2019.
[I-D.ssangli-idr-bgp-vpn-srv6-plus]
Ramachandra, S. and R. Bonica, "BGP based Virtual Private
Network (VPN) Services over SRv6+ enabled IPv6 networks",
draft-ssangli-idr-bgp-vpn-srv6-plus-02 (work in progress),
July 2019.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", STD 89,
RFC 4443, DOI 10.17487/RFC4443, March 2006,
<https://www.rfc-editor.org/info/rfc4443>.
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[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
15.2. Informative References
[I-D.filsfils-spring-net-pgm-extension-srv6-usid]
Filsfils, C., Camarillo, P., Cai, D., Jiang, Z.,
daniel.voyer@bell.ca, d., Shawky, A., Leymann, N.,
Steinberg, D., Zandi, S., Dawra, G., Meilik, I., Uttaro,
J., Jalil, L., So, N., Fiumano, M., and M. Khaddam,
"Network Programming extension: SRv6 uSID instruction",
draft-filsfils-spring-net-pgm-extension-srv6-usid-02 (work
in progress), August 2019.
[I-D.ietf-6man-segment-routing-header]
Filsfils, C., Dukes, D., Previdi, S., Leddy, J.,
Matsushima, S., and d. daniel.voyer@bell.ca, "IPv6 Segment
Routing Header (SRH)", draft-ietf-6man-segment-routing-
header-24 (work in progress), October 2019.
[I-D.ietf-spring-segment-routing-mpls]
Bashandy, A., Filsfils, C., Previdi, S., Decraene, B.,
Litkowski, S., and R. Shakir, "Segment Routing with MPLS
data plane", draft-ietf-spring-segment-routing-mpls-22
(work in progress), May 2019.
[I-D.ietf-spring-srv6-network-programming]
Filsfils, C., Camarillo, P., Leddy, J.,
daniel.voyer@bell.ca, d., Matsushima, S., and Z. Li, "SRv6
Network Programming", draft-ietf-spring-srv6-network-
programming-04 (work in progress), October 2019.
[I-D.li-spring-compressed-srv6-np]
Li, Z., Li, C., Peng, S., Wang, Z., and B. Liu,
"Compressed SRv6 Network Programming", draft-li-spring-
compressed-srv6-np-00 (work in progress), July 2019.
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[I-D.mirsky-6man-unified-id-sr]
Cheng, W., Mirsky, G., Peng, S., Aihua, L., Wan, X., and
C. Wei, "Unified Identifier in IPv6 Segment Routing
Networks", draft-mirsky-6man-unified-id-sr-03 (work in
progress), July 2019.
[RFC2151] Kessler, G. and S. Shepard, "A Primer On Internet and TCP/
IP Tools and Utilities", FYI 30, RFC 2151,
DOI 10.17487/RFC2151, June 1997,
<https://www.rfc-editor.org/info/rfc2151>.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031,
DOI 10.17487/RFC3031, January 2001,
<https://www.rfc-editor.org/info/rfc3031>.
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302,
DOI 10.17487/RFC4302, December 2005,
<https://www.rfc-editor.org/info/rfc4302>.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, DOI 10.17487/RFC4303, December 2005,
<https://www.rfc-editor.org/info/rfc4303>.
[RFC7348] Mahalingam, M., Dutt, D., Duda, K., Agarwal, P., Kreeger,
L., Sridhar, T., Bursell, M., and C. Wright, "Virtual
eXtensible Local Area Network (VXLAN): A Framework for
Overlaying Virtualized Layer 2 Networks over Layer 3
Networks", RFC 7348, DOI 10.17487/RFC7348, August 2014,
<https://www.rfc-editor.org/info/rfc7348>.
[RFC7432] Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February
2015, <https://www.rfc-editor.org/info/rfc7432>.
[RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed.,
"Path MTU Discovery for IP version 6", STD 87, RFC 8201,
DOI 10.17487/RFC8201, July 2017,
<https://www.rfc-editor.org/info/rfc8201>.
Authors' Addresses
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Ron Bonica
Juniper Networks
Herndon, Virginia 20171
USA
Email: rbonica@juniper.net
Shraddha Hegde
Juniper Networks
Embassy Business Park
Bangalore, KA 560093
India
Email: shraddha@juniper.net
Yuji Kamite
NTT Communications Corporation
3-4-1 Shibaura, Minato-ku
Tokyo 108-8118
Japan
Email: y.kamite@ntt.com
Andrew Alston
Liquid Telecom
Nairobi
Kenya
Email: Andrew.Alston@liquidtelecom.com
Daniam Henriques
Liquid Telecom
Johannesburg
South Africa
Email: daniam.henriques@liquidtelecom.com
Luay Jalil
Verizon
Richardson, Texas
USA
Email: luay.jalil@one.verizon.com
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Joel Halpern
Ericsson
P. O. Box 6049
Leesburg, Virginia 20178
USA
Email: joel.halpern@ericsson.com
Jen Linkova
Google
Mountain View, California 94043
USA
Email: furry@google.com
Gang Chen
Baidu
No.10 Xibeiwang East Road Haidian District
Beijing 100193
P.R. China
Email: phdgang@gmail.com
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